The present invention relates to a process for preparing a cosmetic formulation. Historically, cosmetic formulations have been prepared by emulsifying an oil phase with an aqueous phase matrix using a batch process wherein the oil and water mixture is sheared in a large vessel. The oil phase typically includes a mixture of complex and varying oil-miscible ingredients and, consequently, batch-to-batch reproducibility of oil droplet size is often elusive. Moreover, processing time can be quite long and scale-up of the process from the benchtop to the manufacturing plant can be frustrating because tank-based processes often do not scale up in a linear fashion.
In WO 01/54663, Wilmott et al. discloses a possible solution to the problems associated with formulating personal care products by providing a substantially surfactant-free stable aqueous dispersion (that is, stable for at least two months), containing up to 70%, more preferably up to 50%, by weight of an oil phase, to which active ingredients can be added. This approach allows simple mixing of all ingredients, without the need for sub-phases or any special processing, to create a formulated cosmetic product. Nevertheless, there still remains an ever-increasing need to offer formulators more flexibility in controlling and fine tuning the properties of the final product, and to allow the formulators to use dispersions at their convenience.
The present invention addresses a need in the art by providing a process for preparing an advanced cosmetic product comprising the step of contacting a high internal phase ratio (HIPR) emollient-in-water emulsion with a partial cosmetic formulation to produce the advanced cosmetic product.
The process of the present invention reduces significantly the amount of water initially added to the formulated product, thereby providing a distinct advantage to the formulator for controlling the texture, sensation, consistency, shelf stability, and deliverability of active agents of the cosmetic product.
In a second aspect, the present invention is a composition comprising an HIPR silicone elastomer-in-water emulsion.
In a third aspect, the present invention is a composition comprising an HIPR sunscreen agent-in-water emulsion, wherein the sunscreen agent contains at least one chromophoric group absorbing in the ultraviolet range from 290 to 400 nm.
In the process of the present invention, a high internal phase ratio (HIPR) emollient-in-water emulsion is contacted with a partial cosmetic formulation to produce an advanced cosmetic product. In general, HIPR emulsions are characterized by a disperse phase of polyhedral cells at a volume fraction of at least 74% (the most compact arrangement of spheres of equal radius) dispersed in a continuous phase that forms a thin film separating the cells.
As used herein, the word xe2x80x9cemollientxe2x80x9d refers to one or more water-immiscible substances used in cosmetic formulations; the term xe2x80x9cwater-immiscible substancexe2x80x9d refers to a compound capable of forming an HIPR emulsion with water. Examples of emollients include i) mineral oil, petrolatum, polydecene, and isohexadecane; ii) fatty acids and alcohols having from 10 to 30 carbon atoms such as pelargonic, lauric, myristic, palmitic, steraric, isostearic, hydroxystearic, oleic, linoleic, ricinoleic, arachidic, behenic, and euricic acids and alcohols; iii) triglyceride esters such as castor oil, cocoa butter, safflower oil, sunflower oil, jojoba oil, cottonseed oil, corn oil, olive oil, cod liver oil, almond oil, avocado oil, palm oil, sesame oil, squalene, Kikui oil, and soybean oil; iv) acetoglyceride esters such as acetylated monoglycerides; v) ethoxylated glycerides such as ethoxylated glyceryl monostearate; vi) alkyl esters of fatty acids having 10 to 20 carbon atoms such as hexyl laurate, isohexyl laurate, isohexyl palmitate, isopropyl palmitate, decyl oleate, isodecyl oleate, hexadecyl stearate, decyl stearate, diisopropyl adipate, diisohexyl adipate, diisopropyl sebacate, laurly lactate, myristyl lactate, and cetyl lactate; vii) alkenyl esters of fatty acids having 10 to 20 carbon atoms such as oleyl myristate, oleyl stearate, and oleyl oleate; viii) fatty acid esters of ethoxylated fatty alcohols; ix) polhydric alcohol esters such as ethylene glycol mono and di-fatty acid esters, diethylene glycol mon- and di-fatty acid esters, and polyethylene glycol (200-6000) mon- and di-fatty acid esters; x) wax esters such as beeswax, spermaceti, myristyl myristate, and stearyl stearate; xi) silicone oils such as dimethicones and cyclomethicones.
Silicone elastomers constitute yet another class of emollients. These elastomers are advantageously prepared from the crosslinking reaction of a divinyl compound and a polysiloxane compound containing Sixe2x80x94H groups. Examples of commercially available silicone elastomers include General Electric Silicone 1229 (available from General Electric Company) and DC 9040 elastomer (available from Dow Corning Corporation, Midland, Mich.).
For the purposes of the present invention, sunscreen agents are also emollients. A sunscreen agent contains at least one chromophoric group that absorbs in the ultraviolet range of from 290 to 400 nm. Examples of chromophoric organic sunscreen agents include p-aminobenzoic acid as well as salts and esters thereof; o-aminobenzoic acid and o-aminobenzoates (including methyl, menthyl, phenyl, benzyl, phenylethyl, linalyl, terpinyl, and cyclohexenyl esters thereof); salicylic acid and salicylates (including octyl, amyl, phenyl, benzyl, menthyl, glyceryl, and dipropyleneglycol esters thereof); cinnamic acid and derivatives thereof (including menthyl and benzyl esters, alpha-phenyl cinnamonitrile, and butyl cinnamoyl pyruvate); dihydroxycinnamic acid and its derivatives; trihydroxycinnamic acid and its derivatives; diphenylbutadiene and stilbene; dibenzalacetone and benzalacetophenone; naphthosulfonates (such as sodium salts of 2-naphthol-3,6-disulfonic acid and 2-naphthnol-6,8-disulfonic acid); dihydroxynaphthoic acid and its salts; o- and p-hydroxydiphenyldisulfonates; coumarin and derivatives thereof (such as 7-hydroxy, 7-methyl, and 3-phenyl coumarin); diazoles; quinine salts; quinoline and derivatives thereof; hydroxy- or alkoxybenzophenones; uric and vilouric acids; tannic acid and derivatives thereof; hydroquinone; benzophenones (such as oxybenzone, sulisobenzone, dioxybenzone, benzoresorcinol, 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone, 2,2xe2x80x2-dihydroxy-4,4xe2x80x2-dimethoxybenzophenone, octabenzone, 4-isopropyldibenzoylmethane, butylmethoxydibenzoylmethane, etocrylene, and 4-isopropyl-dibenzoylmethane).
Examples of commercially available sunscreen agents are listed in the following table. CTFA refers to Cosmetics, Toiletries, and Fragrances Association.
The HIPR sunscreen-in-water emulsion advantageously includes a stabilizing amount of an additive to prevent Ostwald ripening, that is, to prevent diffusion of the sunscreen active disperse phase from small droplets of the disperse phase to larger ones. The additive is a highly water-insoluble material that 1) has a negligible diffusion coefficient in the continuous aqueous phase and 2) is compatible with the disperse phase (for example, an emollient-phase compatible polymer such a polyisobutene; a long chain paraffin such as hexadecane; or a silicone such as silicone oil or dimethicone.) Preferably the additive is used in an amount not greater 5 weight percent, more preferably not greater than 2 weight percent, based on the weight of the sunscreen agent and the additive.
The HIPR emollient-in-water emulsion is stabilized by a stabilizing amount of a surfactant, which can be internal (that is, where the emollient itself acts as a surface active agent) or external. The concentration of the surfactant is preferably not less than 1% by weight, more preferably not less than 3% by weight, and preferably not more than 20% by weight, more preferably not more than 10% by weight, based on the weight of the emollient phase. External surfactants include nonionic, anionic, or cationic, or combinations of nonionic and anionic or nonionic and cationic.
Examples of nonionic surfactants suitable for stabilizing the HIPR emulsion include polyethylene glycol fatty acid mono- and diesters (such as PEG-8 laurate, PEG-10 oleate, PEG-8 dioleate, and PEG-12 distearate), polyethylene glycol glycerol fatty acid esters (such as PEG-40 glyceryl laurate and PEG-20 glyceryl stearate), alcohol-oil transesterification products (such as PEG-35 castor oil, PEG-25 trioleate, and PEG-60 corn glycerides), polyglycerized fatty acids (such as polyglyceryl-2-oleate and polyglyceryl-10 trioleate), propylene glycol fatty acid esters (such as propylene glycol monolaurate), mono- and diglycerides (such as glyceryl monooleate and glyceryl laurate), sterol and sterol derivatives (such as cholesterol), sorbitan fatty acid esters and polyethylene glycol sorbitan fatty acid esters (such as sorbitan monolaurate and PEG-20 sorbitan monolaurate), polyethylene glycol alkyl ethers (such as PEG-3 oleyl ether and PEG-20 stearyl ether), sugar esters (such as sucrose monopalmitate and sucrose monolaurate), polyethylene glycol alkyl phenols (such as PEG-10-100 nonyl phenol, and PEG-15-100 octyl phenol ether), polyoxyethylene-polyoxypropylene block copolymers (such as poloxamer 108 and poloxamer 182), and lower alcohol fatty acid esters (such as ethyl oleatea and isopropyl myristate).
Examples of suitable ionic surfactants include fatty acid salts (such as sodium laurate and sodium lauryl scarcosinate), bile salts (such as sodium cholate and sodium taurocholate), phospholipids (such as egg/soy lecithin and hydroxylecithin), phosphoric acid esters (such as diethanolammonium polyoxyethylene-10 oleyl ether phosphate), carboxylates (such as ether carboxylates and citric acid esters of mono and diglycerides), acyl lactylates (such as lactylic esters of fatty acids, and propylene glycol aginate), sulfates and sulfonates (such as ethoxylated alkyl sulfates, alkyl benzene sulfones, and acyl taurates), and alkyl, aryl, and alkyl-aryl sulfonates and phosphates. Examples of suitable cationic surfactants include quaternary ammonium salts and hydrochloride salts of N-alkyl diamines and triamines.
The HIPR emulsion can be prepared by a variety of methods, including batch and continuous methods well known in the art. In a preferred continuous method (described generally by Pate et al. in U.S. Pat. No. 5,539,021, column 3, line 15 to column 6, line 27, which passage is incorporated herein by reference) a stream containing the continuous aqueous phase is flowed through a first conduit and merged continuously with a stream of the disperse emollient phase that is flowed through a second conduit. The streams are merged into a disperser in the presence of a stabilizing amount of surfactant. The surfactant can be added to either stream, or as a separate stream, but is preferably added to the stream containing the emollient phase. The rates of the streams are adjusted within the HIPR emulsion region (74% to about 99%) so that particle size and polydispersity of the emulsion are optimized for the particular application. Preferably, the rates of the streams are adjusted so as to produce an HIPR emulsion having an emollient phase-to-aqueous phase ratio of from about 80% to about 95% by volume. The volume-average mean particle size of the emollient phase of the HIPR emulsion is application dependent. Though volume-average mean particle sizes of less than 1 xcexcm are routinely achievable, submicron particle sizes may not be desirable in all cases. Generally, the preferred volume-average mean particle size is not greater than 50 xcexcm, more preferably not greater than 20 xcexcm, more preferably not greater than 10 xcexcm, and most preferably not greater than 2 xcexcm. However, when the emollient is a silicone elastomer, the desired volume-average mean particle size is preferably not less than 2 xcexcm, more preferably not less than 10 xcexcm, and most preferably not less than 20 xcexcm; and preferably not greater than 100 xcexcm, and more preferably not greater than 60 xcexcm.
If the preferred continuous method for preparing the HIPR emulsion is used, the emollient phase must be flowable through the conduit. If the emollient is sufficiently low in viscosity so as to be flowable at ambient temperature and without dilution of solvent, the HIPR emulsion is preferably prepared at ambient temperature and without the use of an ancillary solvent for the emollient. If, on the other hand, the emollient is not flowable through the conduit at ambient temperature, either because it is a solid or a highly viscous liquid at ambient temperature, the emollient can be rendered flowable by either heat or solvent addition. For example, where the emollient is a silicone elastomer, it is desirable to add a solvent for the elastomer in a sufficient amount so as to render the silicone elastomer flowable through the conduit. Preferred solvents for the silicone elastomer include cyclomethicones, dimethicones, or a low viscosity emollient.
Minor amounts, preferably not greater than 5%, more preferably not greater than 1%, and most preferably not greater than 0.5% by weight, of water-compatible substances, that is, substances which, by themselves are incapable of forming aqueous HIPR emulsions, can be added to the emollient prior to emulsification of the emollient. Examples of such water-compatible substances include rheology modifiers such as carbomers, acrylic copolymers, polyacrylamides, polysaccharides, natural gums, and clays; preservatives such as alkyl esters of p-hydroxybenzoic acid; humectants such as glycerol; and pH modifiers.
The HIPR emulsion used in the process of the present invention is combined with a partial cosmetic formulation to produce an advanced cosmetic product. As used herein, xe2x80x9cpartial cosmetic formulationxe2x80x9d refers to one or more finishing ingredients, which, when combined with the HIPR emulsion, form an advanced, and preferably a finished, cosmetic product. The term xe2x80x9cadvanced cosmetic productxe2x80x9d refers to either a finished cosmetic product or one that is closer to being a finished product than before the HIPR emulsion and partial cosmetic formulation were combined. Preferably, the advanced cosmetic product is a finished cosmetic product that is ready to be packaged for and sold to the consumer. In an extreme case, the HIPR emulsion may contain all of the ingredients of the finished product, and the partial cosmetic formulation is simply water. In this case, the HIPR emulsion represents a concentrate of the finished product, which is merely diluted with water to form the finished product.
Although it is possible to prepare an HIPR emulsion that includes the ingredients commonly found in a partial cosmetic formulation such as color, fragrance, rheology modifier, or pH adjuster, it may be desirable to exclude these ingredients from the HIPR emulsion. For example, color, fragrance, rheology, or pH may be more easily controlled when included in the partial cosmetic formulation and combined with an HIPR emulsion that contains predominantly the emulsified emollient. The HIPR emulsion and the partial cosmetic formulation can be combined concomitantly or in any order. Furthermore, more than one HIPR emulsion can be combined with the partial cosmetic formulation to form the advanced cosmetic product. For example, an HIPR emulsion of mineral oil and a separately prepared HIPR emulsion of petrolatum can be combined with a partial cosmetic formulation containing water, thickener, fragrance, and color to form a body lotion. Examples of finished cosmetic products include hand lotion, body lotion, body wash, conditioners, shampoos, and facial creams.
The process of the present invention provides a simple and flexible method of formulating the cosmetic product, due to the ease with which an HIPR emulsion with controlled particle size can be reproduced, to the long shelf-stability of the HIPR emulsion ( greater than 1 year), and to the low quantity of water in the emulsion (less than 26%, and preferably less than 20% by volume, based on the volume of emollient and water).
The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. All percentages are by weight unless otherwise specified. Particle sizes of HIPR emulsions are measured using a Coulter LS 230 Laser Light Scattering Particle Sizer (Coulter Corp.).